Abstract

This paper presents a source model for laser ultrasonic generation in non-metals in the thermoelastic regime. It is shown that the waveforms can be directly related to the optical absorption depth of the material. The longitudinal component due to the buried source is shown to be a bipolar pulse which can be modelled by convolving the temporal form of the laser pulse with the optical absorption profile and its time delayed inverted reflection from the free surface. The heated disc is surrounded by cold constraining material so the radial in-plane forces have Heaviside like time dependence whereas the vertical component only exists during the initial fast rise of the free surface and therefore can be modelled as a delta function. The predications of the model are compared for a TEA CO2 laser generation in a plastic, an Excimer laser in glass and a Nd:YAG laser in silicon. This model also explains difference between constrained and unconstrained surfaces for the first time, in the constrained case the vertical force is related to the integral of the laser pulse profile and has Heaviside like time dependence.